1. Field of the Invention
The present invention relates to a magnetoresistive device and a method of manufacturing the same and to a thin-film magnetic head, a head gimbal assembly, a head arm assembly and a magnetic disk drive each of which incorporates the magnetoresistive device.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of magnetic disk drives has increased. A widely used type of thin-film magnetic head is a composite thin-film magnetic head that has a structure in which a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading are stacked on a substrate.
MR elements include: anisotropic magnetoresistive (AMR) elements utilizing an anisotropic magnetoresistive effect; giant magnetoresistive (GMR) elements utilizing a giant magnetoresistive effect; and tunnel magnetoresistive (TMR) elements utilizing a tunnel magnetoresistive effect.
It is required that the characteristics of a read head include high sensitivity and high output capability. GMR heads incorporating spin-valve GMR elements have been mass-produced as read heads that satisfy such requirements. Recently, developments in read heads using TMR elements have been sought to conform to further improvements in areal recording density.
Conventional GMR heads have a structure in which a current used for detecting magnetic signals (that is hereinafter called a sense current) is fed in the direction parallel to a plane of each layer making up the GMR element. Such a structure is called a current-in-plane (CIP) structure. In the GMR head having the CIP structure, the GMR element is insulated from each of top and bottom shield layers by an insulating film. As a result, there arises a problem that, if the space between the top and bottom shield layers (that is hereinafter called a shield gap length) is reduced to enhance the linear recording density of the GMR head having the CIP structure, the above-mentioned insulating film is made thin and it is therefore difficult to maintain the insulation between the GMR element and each of the shield layers.
To solve such a problem, there have been proposed GMR heads having a structure in which a sense current is fed in the direction perpendicular to a plane of each layer making up the GMR element. Such a structure is called a current-perpendicular-to-plane (CPP) structure. It is not necessary to insulate the GMR element from each of the shield layers for the GMR head having the CPP structure. Therefore, the GMR head having the CPP structure is free from the above-mentioned problem. In addition, the GMR head having the CPP structure has an advantage that, when the track width is reduced, it is capable of producing a greater output than the output of the GMR head having the CIP structure. A TMR head incorporating a TMR element has the CPP structure, too.
In the heads having the CPP structure, a pair of electrode layers for feeding a sense current to the MR element are disposed with a space between the electrode layers in the direction of thickness. The MR element is disposed between the pair of electrode layers. The electrode layers may function as shield layers, too. In this case, the space between the electrode layers is the shield gap length. Typically, bias field applying layers for applying a bias magnetic field to the MR element are disposed on both sides of the MR element, the sides being opposed to each other in the direction of track width. The bias magnetic field directs the direction of magnetization in a layer of the MR element to a specific direction when no signal magnetic field is applied to the MR element, wherein the direction of magnetization in the layer changes in response to a signal magnetic field.
There are some prior-art methods of manufacturing the heads having the CPP structure as will now be described.
A first method is the one disclosed as lift-off in the Published Unexamined Japanese Patent Application 2003-203313 and the Published Unexamined Japanese Patent Application 2003-132509. In this method, an MR film to be an MR element is first formed on a lower electrode layer. Next, a mask is formed on the MR film, and the MR film is selectively etched through the use of the mask to form the MR element. Next, while the mask is left unremoved, an insulating layer is formed to cover the MR element, the mask and the lower electrode layer. The mask is then removed. The top surface of the MR element is thereby exposed. Next, an upper electrode layer is formed on the MR element and the insulating layer.
A second method is the one disclosed as a contact hole method in the Published Unexamined Japanese Patent Application 2003-203313 and the Published Unexamined Japanese Patent Application 2003-132509. This method will now be described with reference to FIG. 27. In the method, an MR film is first formed on a lower electrode layer 101. Next, a mask is formed on the MR film, and the MR film is selectively etched through the use of the mask to form an MR element 102. Next, the mask is removed, and then an insulating layer 103 is formed on the MR element 102 and the lower electrode layer 101. Next, a portion of the insulating layer 103 located on the MR element 102 is selectively etched to form a contact hole 103a. The top surface of the MR element 102 is thereby exposed. Next, an upper electrode layer 104 is formed on the MR element 102 and the insulating layer 103.
A third method is disclosed in the Published Unexamined Japanese Patent Application 2003-203313. This method will now be described with reference to FIG. 28. In the method, an MR film is first formed on the lower electrode layer 101. Next, a mask is formed on the MR film, and the MR film is selectively etched through the use of the mask to form the MR element 102. Next, the mask is removed, and then an insulating layer 105 is formed on the MR element 102 and the lower electrode layer 101. Next, ion beam etching or chemical mechanical polishing (hereinafter referred to as CMP) is performed to remove a portion of the insulating layer 105 located higher than the level of the top surface of the MR element 102 indicated by an alternate long and two short dashes line with numeral 106 in FIG. 28. The top surface of the MR element 102 is thereby exposed and the top surfaces of the MR element 102 and the insulating layer 105 are thereby flattened. Next, an upper electrode layer is formed on the MR element 102 and the insulating layer 105.
A fourth method is disclosed in the Published Unexamined Japanese Patent Application 2003-132509. In this method, an MR film is first formed on a lower electrode layer. Next, a mask is formed on the MR film, and the MR film is selectively etched through the use of the mask to form the MR element. Next, while the mask is left unremoved, an insulating layer is formed to cover the MR element, the mask and the lower electrode layer. Next, the insulating layer is polished until the mask is exposed or immediately before the mask is exposed. If the mask is made of an insulating material, the mask is then removed. If the mask is made of a conductive material, the mask may be removed or left unremoved to be used as a protection layer. Next, an upper electrode layer is formed on the insulating layer and the MR element or the mask.
A fifth method is disclosed in the Published Unexamined Japanese Patent Application 2002-123916. This method will now be described with reference to FIG. 29. In the method, first, an MR film and a conductive protection film are formed one by one on the lower electrode layer 101. Next, a mask is formed on the protection film, and the protection film and the MR film are selectively etched through the use of the mask to form the MR element 102. A protection layer 107 made up of the protection film patterned is disposed on the MR element 102. Next, the mask is removed, and then an insulating layer 108 is formed to cover the MR element 102, the protection layer 107 and the lower electrode layer 101. Next, the insulating layer 108 is polished by CMP until the protection layer 107 is exposed. Next, the upper electrode layer 104 is formed on the protection layer 107 and the insulating layer 108.
Each of the above-described first to fifth methods has problems described below. In the first method, as described in the Published Unexamined Japanese Patent Application 2003-203313 and the Published Unexamined Japanese Patent Application 2003-132509, on the top surface of the MR element, burrs made of unwanted accumulations are formed around the region in which the mask was located and/or the insulating layer overlaps the top surface of the MR element. In either of these cases, it is difficult to form the upper electrode layer having a desired shape with precision.
In the second method, as shown in FIG. 27, a portion of the insulating layer 103 around the contact hole 103a protrudes upward above the top surface of the MR element 102. In this case, too, it is difficult to form the upper electrode layer 104 having a desired shape with precision.
The third method has a problem that it is difficult to precisely remove only the portion of the insulating layer 105 located higher than the level of the top surface of the MR element 102. If the insulating layer 105 remains on the top surface of the MR element 102, it is impossible to electrically connect the MR element 102 to the upper electrode layer 104. On the other hand, if a portion of the MR element 102 is cut away, the property of the MR element 102 is changed.
In the fourth method, when the mask on the MR element is removed, a portion of the insulating layer around the MR element protrudes upward above the top surface of the MR element. In this case, it is difficult to form the upper electrode layer having a desired shape with precision. The fourth method has another problem that, if the mask on the MR element is left unremoved, it is difficult to keep the thickness of the remaining mask unchanged, and it is therefore difficult to keep the shield gap length unchanged.
The fifth method has a problem that it is difficult to maintain the thickness of the protection layer 107 remaining after the insulating layer 108 is polished, and it is therefore difficult to keep the shield gap length unchanged.
In any of the second to fifth methods, the insulating layer is disposed around the MR element, and the top surface of the insulating layer and the top surface of the MR element or the protection layer are located at nearly the same level. As a result, in any of the second to fifth methods, the thick insulating layer is once formed on the MR element or the protection layer, too, in the course of manufacturing process of the head, and the insulating layer is removed by etching or CMP. This causes the above-described problems.